Analyses with TOP-Assay

What is TOP-Assay?

TOP assay (Total Oxidisable Precursor Assay) is a specific laboratory method used in PFAS analysis. It serves to reveal oxidisable PFAS precursors that are often not detected by conventional analyses.  

For this purpose, the precursors are specifically converted into stable, measurable perfluorinated alkyl acids (PFAAs) by means of strong chemical oxidation. The aim is to assess the potential PFAS contamination risk of a sample more comprehensively.

How does the TOP assay work?

The TOP assay is based on alkaline persulphate oxidation, usually using potassium or sodium persulphate. This converts PFAS precursor compounds into short-chain PFAAs that are easy to detect analytically.  

Two analyses are performed for evaluation:

• Native sample: Measurement of existing PFAS.
• Oxidised sample: Measurement after performing the TOP assay.

The difference between the two measurements provides information about the amount of previously undetected, oxidisable PFAS precursors and thus about the PFAS potential of the sample.  

Why is the TOP assay important?

Standard analyses only detect a limited selection of defined individual PFAS substances. Many precursor compounds remain invisible but can transform into persistent PFAS in the environment over the long term.

The advantages of the TOP assay are:

• expands analytical significance,
• provides a more conservative risk assessment,
• is particularly relevant for contaminated sites, AFFF-contaminated sites, groundwater and remediation projects.

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